Minimally-invasive thermal therapies capable of delivering large and varied doses of thermal energy to the body via small catheter based tools offer significant potential to reduce surgical trauma, recovery time, and associated healthcare costs. An inability to effectively monitor the damage fronts created by these techniques, however, has limited their practical application in many arenas. Many investigators have now reported the use of magnetic resonance imaging (MRI) to non-invasively measure temperatures during thermal therapeutic procedures. In phase I, we proposed that MRI could provide temperature information with sufficient temporal, spatial, and thermal resolution to allow for closed-loop feedback control of production of laser-induced thermal therapy lesions. To this end, we designed and constructed a system which utilized near real-time MR images to generate thermal data and to use this data for control of laser lesion production. We subsequently tested the system in both in vitro and in vivo samples with excellent results. In this proposal, we plan to continue development of this laser computer system and to focus it toward two applications for which it is particularly well suited: laser treatment of localized prostate cancer and production of intercranial laser lesions. The end result will be a laser computer system which can be interfaced to a clinical MR scanner during laser surgery and used interactively to guide and control thermal therapy. PROPOSED COMMERCIAL APPLICATION: The direct result of this research will be a commercially viable prototype of a laser computer system which when interfaced to an existing clinical MR scanner, will form a closed-loop feedback controlled thermal therapy system. With some 5000 clinical MR scanners in the US alone, the potential market for such a system should be quite large. In addition, it is likely that medical laser manufacturers as well as makers of other thermal therapies, will incorporate portions of the laser computer into their own platforms in order to make them MR-ready. We have focused initial development of the device toward minimally Invasive treatment of localized prostate cancer where associated health care costs are expected to reach up to $4 billion in 2000.